If I can quell your guilt, I can assure you that in Italy tipping is definitively *not* expected. It's nice if you do, but it's not common (except for exceptional service... or if the server is cute). The only places that expect
tipping are tourist traps that cater to American visitors and travellers.
I was at a trattoria in Siena. I left extra money as a tip and they came running back to me trying to give me my money. I had no idea how to explain that I was giving it to them as a tip. I kept saying "per Lei" and "per tu," but they seemed to just be confused. I finally gave up and took it back.
Then I looked up the word for tip so, when I came back, I was able to say "è una mancia." I know tipping isn't required, but I was shocked at how difficult it was to give one. Now that coppia is ubiquitous (especially in tourist traps) and that can be annoying from my perspective (especially since you can't even get free water), but I'm fine going with what is normal once I know to expect it.